Electrode for electric double layer capacitor

ABSTRACT

In an electrode for an electric double layer capacitor of the present invention, the peak value of particle size distribution of graphite particles added to a conductive adhesive is in a range of 2.6 to 3.2 μm, not less than 100,000 dimples having a largest outer diameter in a range of 4 to 10 μm and a depth in a range of 4 to 15 μm are formed on the surface of the collector sheet per 1 cm 2 , and the occupied area of the dimples to the entire surface area of the collector sheet is not more than 50%. By determining the saponification value of polyvinylalcohol which is used as a binder component of the conductive adhesive in a range of 90.0 to 98.5, adhesiveness of the collector sheet and the electrode forming sheet is improved. Furthermore, by substituting H atoms contained in the polyvinylalcohol with Si atoms, adhesiveness of the collector sheet and the electrode forming sheet can be further improved.

BACKGROUND OF INVENTION

1. Technical Field

The present invention relates to electrodes for electric double layercapacitors which are suitable for use for electric double layercapacitors having large capacity and high power.

2. Background Art

An electric double layer capacitor has characteristics such as longservice life, high cycle characteristics, and characteristics of chargeand discharge with heavy current since there are no chemical reactionsduring charge and discharge of the capacitor as there are in aconventional secondary battery. Therefore, this capacitor is attractingmuch attention as a new type of storage battery or as a driving powersupply automobiles and devices. In particular, an electric double layercapacitor having large capacity and high power is being developed.

As a process for producing such an electric double layer capacitor, amethod in which conductive adhesive is coated on a collector sheet, suchas aluminum foil, and an electrode forming sheet is joined through thisconductive adhesive, is known (see Japanese Unexamined PatentApplication Publication No. 11-162787). In this method, activatedcarbon, conductive carbon, binder, and solvent are mixed and kneadedfirst, and the electrode forming sheet is obtained by rolling anddrying. A conductive filler such as carbon black or graphite and abinder comprising a resin component such as polyvinyl alcohol (PVA) aremixed to prepare a conductive adhesive, and then the conductive adhesiveis coated on the collector sheet and is joined with the electrodeforming sheet and is dried.

It is known that carbon black, which has particles of small diameter,and graphite, which has particles of large diameter, are used togetheras this conductive filler in order to maintain adhesive strength byincreasing contact surface area with small particles, and in order tomaintain macro conductive paths with large particles (see JapaneseUnexamined Patent Application Publication No. 7-201663.

Furthermore, since water-based solvent is used in the conductiveadhesive using PVA in the above-mentioned process for production of theelectrode for electric double layer capacitor, preparation is easy, itis not necessary to use harmful organic solvents, reducing environmentalmeasures, the cost is low, and durability is superior.

However, there is a problem in that the initial resistance of thecapacitor cannot be restrained only by using carbon black and graphitetogether, and there is also a problem in that adhesive strength is notimproved. There are even cases in which efficiency is deteriorated. Itshould be noted that there is no description of the kind of carbon blackand graphite which may be used in the above patent applicationpublication. Furthermore, in the case in which it is used as a drivingpower source of a car, the temperature of the electrolyte is increasedsince the capacitor is used under severe conditions, and there is aproblem of interface separation caused by deterioration of adhesivestrength.

Furthermore, there is a problem in that a water based adhesive such asPVA may be easily affected by, for example, surface properties ofadhering material or temperature, and adhesive strength may easilybecome unstable. If adhesive strength becomes unstable, the collectorsheet and a layer comprising conductive adhesive (hereinafter referredto as a conductive adhesive layer) may be easily separated along theinterface, and the interface resistance is increased while charging anddischarging. In particular, in a case in which the capacitor is used asa driving power resource of a car, the temperature of the electrolyte isincreased under severe conditions, and interface separation may easilyoccur.

SUMMARY OF THE INVENTION

The present invention was completed in view of the situation describedabove, and an object of the present invention is to provide an electrodefor an electric double layer capacitor in which initial resistance of acell can be restrained by optimizing the diameter of graphite particleswhich is the conductive filler of the conductive adhesive, and increaseof resistance with aging can be restrained by maintaining adhesivestrength. Furthermore, an object of the present invention is to providean electrode for an electric double layer capacitor in which increasingof resistance can be restrained by improving adhesive property of thecollector sheet and the electrode forming sheet of the electrode forelectric double layer capacitor in which PVA is used as a resincomponent of the conductive adhesive.

The electrode for an electric double layer capacitor of the presentinvention which comprises a conductive adhesive layer comprising carbonblack, graphite, and binder between the collector sheet and theelectrode forming sheet has not fewer than 100,000 dimples having alargest outer diameter in a range of 4 to 10 μm and a depth in a rangeof 4 to 15 μm formed on the surface of the above-mentioned collectorsheet per 1 cm², the occupied area of the dimples relative to the entiresurface area of the collector sheet is not more than 50%, and the peakvalue in the particle size distribution of the graphite is in a range of2.6 to 3.2 μm.

The graphite having a peak value in the particle size distribution in arange of 2.6 to 3.2 μm of the present invention can maintain macroconductive paths, and can also improve adhesiveness by desirablyentering into the dimples formed on the surface of the collector sheet.In the case in which the peak value in the particle size distribution isbelow the range, graphite cannot behave as a carbon particle of largediameter any longer, macro conductive paths may be lost, and resistivityof the conductive adhesive may be increased. On the other hand, in thecase in which the peak value in the particle size distribution is abovethe range, contact area among the particles may be reduced, and it maybecome difficult for graphite to enter into the dimples formed on thesurface of the collector sheet, adhesive strength may be deteriorated,and interface separation may easily occur.

In the electrode for an electric double layer capacitor of the presentinvention having the structure mentioned above, since the peak value inthe particle size distribution is in a range of 2.6 to 3.2 μm, macroconductive paths can be desirably maintained, and initial resistance ofthe cell can be sufficiently restrained. At the same time, since thegraphite having the peak value in the particle size distributionmentioned above can enter into the dimples formed on the surface of thecollector sheet, adhesive strength is improved compared to before, andas a result, increasing of resistance by aging can be restrained.

The surface characteristics of the collector sheet of the presentinvention are such that not fewer than 100,000 dimples having a largestouter diameter in a range of 4 to 10 μm and a depth in a range of 4 to15 μm are formed on the surface per unit area (1 cm²), and the occupiedratio of the area of the dimples to the entirety of the collector sheetis not more than 50%. As the collector sheet of the present invention,various kinds of metallic foil can be used. Generally, aluminum foil isdesirable. Particularly in the present invention, aluminum foil in whichetching process is performed on the surface is used. This etchingprocess forms fine dimples on the surface, and carbon particles of theconductive adhesive enter into these dimples and adhere strongly, andthus the interface separation of the conductive adhesive and thecollector sheet can be restrained. FIG. 1 is a drawing showing suchcollector sheet and electrode forming sheet joined by the conductiveadhesive in the present invention. FIGS. 2 and 3 are electronmicrographs showing the aluminum foil used in the present invention.FIG. 2 is an electron micrograph showing the surface of the aluminumfoil whose surface is etched, and it is clear that fine dimples areformed. FIG. 3 is an electron micrograph showing a cross section of thealuminum foil in which etching is performed, and the depths of thedimples are shown.

Furthermore, another aspect of an electrode for electric double layercapacitor of the present invention in which a conductive adhesive layercomprising conductive filler and PVA is formed between the collectorsheet and the electrode forming sheet is that the saponification valueof the PVA is in a range of 90.0 to 98.5.

Generally, PVA is synthesized by a method as follows: vinyl acetate issynthesized by reacting acetic acid and ethylene in the presence ofoxygen; vinyl acetate is polymerized to generate polyvinyl acetate; andalkali is added to this polymer to saponify the acetic group (CH₃COO—)of polyvinyl acetate into a hydroxyl group (OH). However, in the case inwhich all the acetic groups are saponified, problems of preservation canbe considered since the polymer becomes insoluble in water, and thepolymer is easily gelatinized. Therefore, in an actual process forproduction of PVA, PVA is produced under the conditions shown inChemical Formula 1 in which the acetic group and the hydroxyl group bothexist. The ratio of the hydroxyl group to the total number of bothfunctional groups is defined as the saponification value.

In the conductive adhesive of the present invention having the structuredescribed above, since the saponification value of PVA is in a range of90.0 to 98.5, the remaining ratio of acetic groups is extremely low, andswelling of the conductive adhesive layer by propylene carbonate (PC)which is an electrolyte can be restrained. As a result, adhesivestrength is improved.

By using such conductive adhesive, the collector sheet and the electrodeforming sheet are desirably adhered. Furthermore, since water can beused as a solvent, the solvent can be removed by minimal heating duringa drying process, and embrittlement of the electrode by heat can berestrained.

Aspects of the present invention are further explained in detail.

It is desirable that the conductive adhesive of the present inventioncomprise a conductive filler, a binder, and a dispersant. As theconductive filler, carbon based particles such as carbon black orgraphite are desirable. Furthermore, it is desirable that conductivecarbon particles having large diameter and small diameter both becontained.

Since the carbon particles of large diameters can maintain macroconductive paths, resistivity of the conductive adhesive can be reduced,and initial resistance of a cell can be sufficiently restrained.However, in the case in which only carbon particles of large diametersare used, in spite of the fact that the macro conductive paths can bemaintained, adhesive strength and contact area are poor, and separationalong the adhering interface may easily occur.

On the other hand, in the case in which only carbon particles of smalldiameters are used, since the particles can be densely filled, this isdesirable from the viewpoints of adhesive strength and contact area.However, if few macro conductive paths are contained, resistivity of theconductive adhesive may increase. Therefore, it is desirable thatconductive particles of large diameters and small diameters both becontained.

In the conductive adhesive of the present invention, graphite is addedas the carbon particle of large diameter and carbon black is added asthe carbon particle of small diameter. It is desirable that thecontained ratio be in a range of 30:70 to 70:30, and in the presentinvention, they are added at a more desirable ratio of 55:45.

Polyvinyl alcohol is added as a binder of the conductive adhesive of thepresent invention; however, it need not be so limited. Other resins suchas polyvinyl acetate, polyacrylic acid ester, copolymer of ethylenevinyl acetate, ionomer resin, polyvinyl butyral, nitro cellulose,styrene butadiene rubber, butadiene acrylonitrile rubber, neoprenerubber, phenol resin, melamine resin, polyurethane resin, urea resin,polyimide resin, or polyamideimide resin can be used.

As a solvent of the conductive adhesive of the present invention, otherthan water, solvents such as methanol, ethanol, isopropyl alcohol,butanol, trichloroethylene, dimethylformamide, ethylether, or acetonecan be used alone or in combination.

In the conductive adhesive of the present invention,carboxymethylcellulose (CMC) is used as a dispersant. This is added toprevent carbon black and graphite, which are conductive fillers frombeing agglutinated.

Furthermore, the present invention is characterized in that thesaponification value of PVA, which is a binder, is in a range of 90.0 to98.5. PVA generally has acetic groups and hydroxyl groups in itsproduction process as described above. In the case in which thisremaining acetic group is contained in large amounts (case of lowsaponification value), the conductive adhesive layer is swelled by theelectrolyte, and separation between the collector sheet and conductiveadhesive layer may easily occur. On the other hand, in the case in whichthe saponification value is above the range, gelatinization may easilyoccur, and durability is extremely low. Therefore, it is desirable thatthe saponification value of PVA be in the range of the presentinvention.

Furthermore, in the present invention, it is desirable that 0.5 to 2.0%of H atoms of hydroxyl groups contained in PVA of the binder besubstituted by Si atoms. That is, metals such as aluminum or the likegenerally form a skin containing hydroxide on its surface, although inthe case of the PVA having structure mentioned above, since Si atoms ofPVA bond with the hydroxyl group of the skin which is formed on thesurface of aluminum foil which is the collector sheet, adhesiveness maybe further improved. Therefore, even a PVA having a low saponificationvalue can restrain separation of the conductive adhesive layer and thecollector sheet. To obtain such effect, not less than 0.5% of H atomsmust be substituted by Si atoms, and the adhesiveness is improved as thesubstitution ratio of Si is increased. However, in the case in which theratio of Si substitution is greater than 2.0%, solubility in water maybe decreased, and preparation of the adhesive becomes difficult.Therefore, it is desirable that the substitution ratio of H atoms by Siatoms be in a range of 0.5 to 2.0%.

As the collector sheet of the present invention, various kinds of metalcan be used, and aluminum foil is generally desirable. Particularly inthe present invention, aluminum foil whose surface is etched is used.Carbon particles in the conductive adhesive enter into fine pitting ofthe surface formed by this etching process to adhere strongly, and thusthe interface separation of the conductive adhesive and the collectorsheet can be restrained. The collector sheet of the present inventiondesirably has surface characteristics that not fewer than 100,000pittings having a diameter in a range of 4 to 10 μm and a depth in arange of 4 to 15 μm are formed on the surface per unit area (1 cm²), andthat the occupied ratio of the area of the dimples to the entirety ofthe collector sheet is not more than 50%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing showing a collector sheet and electrode formingsheet joined by a conductive adhesive in the present invention.

FIG. 2 is an electron micrograph showing a surface of the etchedaluminum foil of an Example.

FIG. 3 is an electron micrograph showing a cross section of the etchedaluminum foil of an Example.

FIG. 4 is a graph showing the relationship of graphite particle diameter(peak value in the particle distribution) and the cell resistance of anExample.

FIG. 5 is a graph showing the relationship of graphite particle diameter(peak value in the particle distribution) and the increased ratio ofresistance of an Example.

FIG. 6 is a graph showing the relationship of the saponification valueof PVA and the fraction of defective of cells of the electrode forelectric double layer capacitor of an Example.

EXAMPLES

The present invention is further explained by way of Examples. However,the present invention is not limited thereto.

Example 1

1. Measurement of Particle Size Distribution of Graphite

To prepare electric double layer capacitors in which the diameter ofgraphite used is varied, particle size distributions of graphite weremeasured first. 0.1 g of Samples (graphite) A to J were added to asolvent in which 10 g of isopropyl alcohol and 10 g of water were mixed,dispersed uniformly by ultrasonic waves of 38 kHz for 10 minutes, andthe particle size distribution was measured by a microtrac particle sizeanalyzer (trade name: HRA MODEL 9320-X100, produced by NIKKISO Co.,Ltd.). Measurement was performed three times per Sample, 30 seconds eachtime. The average value of the obtained data was measured.

The peak values of the particle size distributions of Samples A to J ofthe above-mentioned measured Sample (graphite) were 2.0 μm, 2.3 μm, 2.5μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 4.0 μm, 5.0 μm, and 10.0 μm. TheseSamples were used as raw materials of conductive adhesives A to J.

2. Mixing of Conductive Adhesive

The following raw materials were mixed and blended to obtain conductiveadhesive of Examples. It should be noted that the graphite used in theconductive adhesives A to J was the graphite having a peak value ofparticle size distribution in a range of 2.0 to 10.0 μm mentioned in themeasurement above.

-   Polyvinyl alcohol (trade name: Kuraray Poval R-1130, produced by    KURARAY Co., Ltd.): 3 weight %-   Carbon black (particle diameter 0.2 μm, produced by DENKI KAGAKU    KOGYO K. K.): 10 weight %-   Graphites A to J (particle diameter 2.0 to 10 μm, produced by NIPPON    GRAPHITE INDUSTRIES, Ltd.): 10 weight %-   Carboxymethylcellulose (dispersant, produced by DAI-ICHI KOGYO    SEIYAKU Co., Ltd.): 3 weight %-   Pure water: 74 weight %    3. Preparation of Electrode Forming Sheet

The following raw materials were mixed and blended to disperse the rawmaterial powder uniformly. The mixture was put in a kneading device, acombining process by double axes was performed for 10 minutes underconditions of 0.5±0.05 MPa, to obtain a solid material. The solidmaterial was pulverized to obtain pulverized powder. The pulverizedpowder was applied to pre-sheet forming by using calender rolling. Thethickness of the sheet was controlled by a rolling process using arolling roll, to obtain the electrode forming sheet of Example.

-   Activated carbon powder (trade name: KH-1200, produced by KUREHA    CHEMICAL INDUSTRIES Co., Ltd.): 80 weight %-   Conductive carbon (trade name: Denkablack, produced by DENKI KAGAKU    KOGYO K. K.): 10 weight %-   PTFE resin (trade name: Teflon (trade mark) 6J, produced by DU    PONT-MITSUI FLUOROCHEMICALS CO., LTD.): 10 weight %    4. Preparation of Electrode

The above-mentioned conductive adhesive A was coated on the surface of along etched aluminum foil (trade name: ED-402H, produced by NIPPONCHEMI-CON CORPORATION) by a gravure roller, the above-mentionedelectrode forming sheets was joined with the aluminum foil and pressedby a roll press at a nip pressure of 0.1 MPa. This sheet was dried byvacuum drying at 160° C. for 12 hours to obtain electrode A of anExample. Furthermore, except that conductive adhesives B to J were usedinstead of conductive adhesive A, electrodes B to J of Examples wereprepared in the same way as described above.

5. Evaluation of Examples

When electric double layer capacitors are used connected in series in acar, deterioration of efficiency of charge and discharge over time isundesirable. Therefore, durability tests of single cells of the electricdouble layer capacitor in which each electrodes A to J of the Exampleswere used was performed. The durability test was performed by applying2.5 V for 2000 hours at 45° C. Initial resistance of each single celland measured results of increased ratio of resistance after thedurability test are shown in Table 1. Values of initial resistance arenot actual values, but minimum values among electrodes A to J defined as100, and relative values are shown. Similarly, values of resistanceafter durability tests are also relative values to the values of initialresistance which is defined as 100. TABLE 1 Peak value in the parti- clesize distribution Cell resistance Cell resistance of graphite (μm)(initial) (after 1000 hours) Electrode A 2.0 150 — Electrode B 2.3 110 —Electrode C 2.5 105 — Electrode D 2.8 100 110 Electrode E 3.0 100 110Electrode F 3.2 100 110 Electrode G 3.5 100 120 Electrode H 4.0 100 135Electrode I 5.0 100 145 Electrode J 10.0 100 —

High initial resistance was observed in the case of electrodes A to C.It is thought that macro conductive paths were not formed since theparticle diameters of the graphite were too small. Resistance increaseafter the durability test was extreme in the case of electrodes G to I.It is thought that adhesive strength with the collector sheet wasinsufficient, and separation occurred along the joining interface sincethe particle diameters of graphite were too large. Similarly, in thecase of electrode J, it is thought that adhesive strength with thecollector sheet was insufficient, and separation occurred along thejoining interface after the durability test since the particle diametersof graphite were too large.

FIG. 4 is a graph showing the relationship of graphite diameter (peakvalue in the particle distribution) contained in the electric doublelayer capacitor of the Examples and the cell initial resistance ofExamples. As is described above, efficient initial resistance can beexhibited since macro conductive paths can be maintained when theparticle diameters of graphite are large. In the present invention, itcan be said that diameters not less than 2.6 μm are desirable.

FIG. 5 is a graph showing the relationship of graphite diameter (peakvalue in the particle distribution) contained in the electric doublelayer capacitor of the Examples and the increased ratio of resistanceover time of the durability test. As is described above, it is obviousthat the increased ratio of resistance can be restrained since thegraphite enters into dimples of the collector sheet to adhere stronglywhen the diameters of the graphite are small. In the present invention,it can be said that a diameter of not more than 3.2 μm is desirable.

Example 2

1. Preparation of Conductive Adhesive

3 parts by weight of polyvinylalcohol having a saponification value of98.5, 10 parts by weight of carbon black (trade name: Denkablack,produced by DENKI KAGAKU KOGYO K.K.), 10 parts by weight of graphite(trade name: SP-300, produced by NIPPON GRAPHITE INDUSTRIES, Ltd.), 3parts by weight of carboxymethylcellulose (trade name: Celogen F-3H,produced by DAI-ICHI KOGYO SEIYAKU Co., Ltd.), and 74 parts by weight ofpure water were mixed and agitated to obtain the conductive adhesive ofExample 2.

2. Preparation of Electrode Forming Sheet

80 parts by weight of activated carbon powder (trade name: KH-1200,produced by KUREHA CHEMICAL INDUSTRIES Co., Ltd.), 10 parts by weight ofconductive carbon (trade name: Denkablack, produced by DENKI KAGAKUKOGYO K. K.), and 10 parts by weight of PTFE resin (trade name: Teflon(trade mark) 6J, produced by DU PONT-MITSUI FLUOROCHEMICALS Co., Ltd.)were mixed and agitated to disperse the raw material powder uniformly.The mixture was put in a kneading device, a combining process by doubleaxes was performed for 10 minutes under conditions of 0.5±0.05 MPa, toobtain a solid material. This solid material was pulverized to obtainpulverized powder. This pulverized powder was applied to pre-sheetforming by using calender roll. The thickness of the sheet wascontrolled by a rolling process using a rolling roller, to obtain theelectrode forming sheet.

3. Preparation of Electrode

The above-mentioned conductive adhesive was coated on the surface of along etched aluminum foil (trade name: ED-402H, produced by NIPPONCHEMI-CON CORPORATION) by a gravure roll, the above-mentioned electrodeforming sheets was joined with the aluminum foil and pressed by a rollpress. This sheet was dried by vacuum drying at 160° C. for 72 hours toobtain an electrode.

Next, electrodes of Examples 3 to 7 and Comparative Examples 1 to 6 wereprepared in the conditions described below.

Example 3

Except that the saponification value of polyvinylalcohol was 95,electrode was prepared in the same way as in Example 2.

Example 4

Except that the saponification value of polyvinylalcohol was 92,electrode was prepared in the same way as in Example 2.

Example 5

Except that the saponification value of polyvinylalcohol was 90,electrode was prepared in the same way as in Example 2.

Comparative Example 1

Except that the saponification value of polyvinylalcohol was 88,electrode was prepared in the same way as in Example 2.

Comparative Example 2

Except that the saponification value of polyvinylalcohol was 85,electrode was prepared in the same way as in Example 2.

Comparative Example 3

Except that the saponification value of polyvinylalcohol was 80,electrode was prepared in the same way as in Example 2.

Comparative Example 4

Except that the saponification value of polyvinylalcohol was 99,electrode was prepared in the same way as in Example 2. However,durability was poor and gelatinization occurred, making it impossible toprepare an electrode.

Example 6

Except that polyvinylalcohol in which the saponification value was 92and 2% of H atoms was substituted by Si atoms was used instead ofpolyvinylalcohol having a saponification value of 98.5, electrode wasprepared in the same way as in Example 2.

Example 7

Except that polyvinylalcohol in which the saponification value was 90and 2% of H atoms was substituted by Si atoms was used instead ofpolyvinylalcohol having a saponification value of 98.5, electrode wasprepared in the same way as in Example 2.

Comparative Example 5

Except that polyvinylalcohol in which the saponification value was 88and 2% of H atoms was substituted by Si atoms was used instead ofpolyvinylalcohol having the saponification value of 98.5, electrode wasprepared in the same way as in Example 2.

Comparative Example 6

Except that polyvinylalcohol in which the saponification value was 85and 2% of H atoms was substituted by Si atoms was used instead ofpolyvinylalcohol having a saponification value of 98.5, electrode wasprepared in the same way as in Example 2.

Evaluation of Examples 2 to 7 and Comparative Examples 1 to 6

When an electric double layer capacitor is used connected in series in acar, deterioration of efficiency of charge and discharge over time isundesirable. Therefore, durability tests of single cells of the electricdouble layer capacitor in which each electrode of Examples 2 to 7 andComparative Examples 1 to 6 were used was performed. The durability testwas performed by applying 2.5 V for 2000 hours at 45° C. After the test,a cell in which increased ratio of resistance to initial resistance wasless than 20% was evaluated as non-defective, and a cell in which theincreased ratio was not less than 20% was evaluated as defective.Results are shown in FIG. 6. It is obvious that PVA in which H atoms ofthe hydroxyl group are substituted by Si atoms can restrain rate ofdefective cells even if the saponification value of the PVA is low. Itis thought that this is because Si atoms bond to hydroxyl groups of thesurface of the aluminum.

As explained above, the present invention has not less than 100,000dimples having a largest outer diameter in a range of 4 to 10 μm and adepth in a range of 4 to 15 μm are formed on the surface of thecollector sheet per 1 cm², the occupied area of the dimples to theentire surface area of the collector sheet is not more than 50%, and thepeak value in the particle size distribution of the graphite is in arange of 2.6 to 3.2 μm. By this invention, electrodes for electricdouble layer capacitor in which initial resistance can be sufficientlyrestrained and increase of resistance over time can be restrained can beprovided.

Furthermore, by improving adhesiveness of the collector sheet and theelectrode forming sheet of electric double layer capacitor in which PVAis used as a resin component of conductive adhesive, electrode forelectric double layer capacitor in which increase of resistance can berestrained can be provided.

1. (canceled)
 2. An electrode for an electric double layer capacitor,comprising: a collector sheet; an electrode forming sheet; a conductiveadhesive layer comprising conductive filler and polyvinylalcohol betweenthe collector sheet and the electrode forming sheet; and asaponification value of the polyvinylalcohol in a range from 90.0 to98.5.
 3. The electrode for electric layer capacitor according to claim2, wherein 0.5 to 2.0% of hydrogen of hydroxyl groups contained in thepolyvinylalcohol is substituted by silicon.
 4. (canceled)